Electron optic device for a beam propagating perpendicularly to crossed magnetic and electric fields



June 8, 1954 o. DOHLER ETAL 2,680,823 ELECTRON OPTIC DEVICE FOR A BEAMPROPAGATING PERPENDICULARLY TO CROSSED MAGNETIC AND ELECTRIC FIELDSFiled July 1, 1950 3 Sheets-Sheet 1 DOHLER ET AL 7 2,680,823 DEVICE FORA BEAM PROPAGATING June 8, 1954 ELECTRON OPTIC PERPENDICULARLY TOCROSSED MAGNETIC AND ELECTRIC FIELDS s Sheets-Sheet 2 Filed July 1, 1950June 8, 1954 OHLER ET AL 2,680,823

0. D ELECTRON OPTIC DEVICE FOR A BEAM PROPAGATING PERPENDICULARLY TOCROSSED MAGNETIC AND ELECTRIC FIELDS Filed July 1, 1950 3 Sheets-Sheet 3Patented June 8, 1954 UNITED STATES PATENT OFFICE ELECTRON OPTIC DEVICEFOR A BEAM PROPAGATING PERPENDICULARLY TO CROSSED MAGNETIC AND ELECTRICFIELDS Oscar Diihler and Alfred Lerbs, Paris, France, as-

signors to Compagnie Generale de Telegraphic Sans Fil, a corporation ofFrance Application July 1, 1950, Serial No. 171,706 Claims priority,application France July 7, 1949 '7 Claims. (Cl. 313-75) in suchconditions the paths of electrons are cycloidal, that is to say thatsaid electrons return periodically to the potential of the cathode as inthe static case of the magnetron.

It is known that the efiiciency and gain of a tube functioning with sucha beam are proportionally as much greater as the amplitude of thecycloidal movement is weaker, and the present invention is directedtowards the means of reducing said amplitude in such a manner that themovement of the electrons becomes as rectilinear as possible.

A means considered in the present invention consists of a progressivevariation along the beam, of the relation between the electric andmagnetic field, by operating on either one or the other of said fields,or on both.

A further object of the present invention is to reduce as much aspossible the length of the transitory space occupied by the electronoptics in which the movement of the electrons loses A progressively itscycloidal characteristic, and consists of an adequate arrangement at thesource of the electronic beam.

' The present invention will be better understood by means of theannexed drawings:

Fig. 1, diagram showing the electronic paths.

Figs. 2 and 3, a system employing the means conforming to the presentinvention.

Figs. 4 and 5, two other embodiments of a sec- .ond system.

Fig. 6, a form of cylindrical construction.

Figs. 7, 8, 9 and 10, four systems relative to the arrangement of thecathode, employing further means conforming to the present invention.

Fig. 1 represents schematically a system comprising anode A and cathodeC between which is applied an electric field, a magnetic field B beingapplied perpendicularly relative to the plan of the drawing. A powersource C, situated at the level of cathode C and connected to thepotential of said cathode, produces a beam of electrons which travelperpendicularly between A and C in theelectric and magnetic field. Inthe known devices, where the distance between A and C is constant, theelectrons follow cycloidal paths as shown by a. It is of advantage forthe efficiency and gain that the electrons follow the rectilinear path(1. The means conforming to the present invention assure that theelectrons follow, if not the ideal path d, at least the intermediarypaths bor c, or that the form of said paths approach gradually towardsd, on passing progressively by b and c.

The present invention is based on the fact that the form of the paths ofelectrons is influenced by the ratio 13/13 and that the amplitude ofcycloidal movement becomes reduced in proportion to the increase of saidratio. According to the present invention there is therefore provided anelectron optics device in which said ratio increases progressively inthe direction of the beam propagation.

A system represented in Fig. 2 in cross section, and in Fig. 3, planview comprises means for diminishing progressively the magnetic field inthe direction of the propagation of the beam and P2 with an appropriateprofile along the portion I on which is effected the progressivetransformation of the cycloidal path e into a rectilinear path. Theremaining references shown in Figs. 2 and 3 have the same significationas in Fig. 1. For purposes of comparison there is indicated in dottedlines the cycloid followed by the electrons with the same constantfields in the homogeneous space between electrodes A and C.

In practice it is easier to increase the electric field rather then todecrease the magnetic field in the direction of the propagation of thebeam. Figs. 4 and 5 show simple forms of an electron optics effectingsaid increase. The same references designating thesame elements as inthe preceding figures there is obtained, on bending to an angle a thenegative electrode in Fig. 4 or the anode in Fig. 5. If the distancebetween cathode C and space 2 where the fields E. and B are homogeneousis great enough, the beam will be sufiiciently linear on entering intospace 2 even if the amplitude of the cycloidal movement at the beginningof space I is relatively great. Any type of cathode can therefore beutilised, either plane oxide cathodes or directly heated or a filamentthe initial direction of the electrons, determining the beginning of thepath being unimportant since whatever the initial path may be it hassufficient time to become linear before entering the homogeneous space.

The linear arrangements according to Figs. 4 and 5 have often thedisadvantage of being too long. A means of avoiding this disadvantageconsists of constructing the device in cylinder form, as shown in Fig.6.

Fig. 6 shows delay line H incoming at E and outgoing at S. Said delayline is at the same potential as anode A of the heretofore describedelectron optics device which comprised the same elements A, C, C,excepting that the electrodes are suitably incurved in order to injectthe beam into the circular space between H and C, at the same timeretaining the basic arrangement of Fig. 4. Collector P receives theelectrons which are not absorbed by H. A power source C, and a negativeelectrode are of the same potential. The distance between C and Adecreasing towards the constant distance between H and C the electricfield increased in space i. The electron optic corresponding to saidspace is therefore in the non utilised space of the interior of housingT,

of which latter no dimension need be changed.

A further means of reducing the length of space I in Figs. 4 and 5consists of providing the cathode with a form and position in such amanner that the initial directions of the emission of electrons arefavorable to the rapid transforma tion of their paths into a straightline, the amplitude of the cycloidal movement being greatly reduced atthe point of departure from said cathode.

Fig. 7, representing the arrangement and references of Fig. 4, shows theemitting surface of cathode C practically perpendicular in relation topath e. Nevertheless, if the surface of said cathode is plane and largeenough (in the case where a strong emitting current is required), thepaths will be approximately linear according to the point of emission ofsaid cathode. To avoid this efiect, the surface of said cathode isprovided curved, as shown in Fig. 8, said curve being determinedexperimentally in such a manner that the paths rapidly assume a linearform independent of the point of emission. This effect can also belessened by choosing a suitable angle 5 which forms said cathode surfacewith negative electrode C.

A further means of obtaining a distribution of the electric fieldfiavorising the formation of a linear beam is shown in Fig. 9. Negativeelectrode C is divided into two electrodes C and C",

of which C is connected to power source C,

whereas C" is at negative potential in relation to C. The intensity ofthe electric field increases in the direction of arrow 1. Said fielddistribution is therefore not determined by the form of the electrodesas in Figs. 4 to 8,. but by the distribution of the tension between theelectrodes. The advantage of this arrangement is that it allows thechoice of a desired position of the beam in space 2 and the possibilityof influencing, in a certain degree, the shape of the focusing field andconsequently the focusing of the beam.

It is obvious that the form and arrangements of the cathode in Figs. 7and 8 can be applied to Fig. 9. The arrangements shown in Figs. '7 and 8can. also be combined with the arrangements shown in Fig. 4, thusobtaining the arrangement shown in Fig. 10, said Fig. 10 beingunderstood without any further description, the reference utilised beingthe same as in the preceding figures.

The present invention is applicable to all tubes where the electronicbeam moves perpendicularly to crossed electric and magnetic fields andparticularly to those where at least one of the electric fieldelectrodes is in the form of a delay line in which is propagated,parallel to said beam, an electromagnetic wave intended to be amplified.The different forms of application and embodiment of the presentinvention as represented in the annexed drawings are not limitative buton the contrary allow all the variations accessible to anyone skilled inthe relevant art, particularly relative to the design and arrangement ofthe cathode and the means to be utilised to focus the emission of saidcathode in a predetermined direction.

What We claim is:

1. An electronic tube comprising a pair of electrodes extendingsubstantially parallel over a part of the tube length and provided withconnections to a potential source to establish an electric field betweensaid electrodes, an electronic gun situated close to the beginning ofthe space between said electrodes and comprising means for injectinginto said space an electronic beam essentially perpendicular to saidelectric field, means comprising a magnetic circuit for causing asubstantially time-constant magnetic field to traverse said space in adirection perpene dicular to said electric field and to said beam, andmeans to cause the ratio between the intensities of said electric andsaid magnetic field to increase in said direction of propagation, theintensity of the magnetic field and the difference of potentials betweensaid electrodes remaining constant over the other part of the length ofsaid space.

2. Electronic tube according to claim 1, in which the magnetic circuitcomprises a gap which increases in the direction of the propagation ofthe beam.

3. Electronic tube according to claim 1, in which the distance betweenthe electrodes decreases in the direction of the propagation of thebeam, at least in the vicinity of the entry of said beam into the spacebetween said electrodes.

4. Electronic tube according to claim 1, in which one of the electrodes,in the vicinity of the entry of the beam into the space between saidelectrodes is divided into several portions conneoted to differentpotentials relating to the second electrode.

5. Electronic tube according to claim 1, in which at. least one of theelectrodes, in the vicinityof the entry of the beam into the spacebetween the electrodes, is bent at a certain angle in relation to thesecond electrode.

6. Electronic tube according to claim 5, in which the electronic gun issituated at a certain part of the bent electrode, said part being bentat a right angle in relation to the part of the same electrodedelimiting the entrance of the space traversed by the beam.

7. Electronic tube according to claim 6, in which the part of theelectrode containing the electronic gun is concave in the direction ofthe beam.

References Cited in the file of this patent UNITED STATES PATENTSBackmark et al. Jan. 2, 1951

